The subject matter disclosed herein relates generally to the field of interference mitigation in wireless embedded systems.
Short-range wireless networks operate in a license-free frequency band, which may vary by geographical region. For example, in the United States, the 902 MHz to 928 MHz frequency band is part of the unlicensed industrial, scientific, and medical (ISM) band designated by the federal communications commission (FCC). This band is occupied by a wide variety of wireless devices, such as cordless phones, wireless meter reading system, home automation systems, etc. Because wireless embedded systems transmit signals with relatively low power to conserve battery life, interference between multiple radiofrequency (RF) sources may cause unreliable operation of wireless embedded systems.
Spread spectrum techniques including frequency hopping and direct sequence spread spectrum, may be employed at the transceiver hardware level to enhance the robustness of network against interference from outside signal sources. However, non-random, continuous or periodic interference from other wireless devices operating in a slice of the same frequency band may yield deteriorated performance in channels that overlap with interfering sources. Moreover, using frequency hopping and direct sequence spread spectrum can be energy-intensive and therefore not always practical for battery operated wireless devices. Other methods of overcoming interference include forming a hierarchical branching tree of wireless devices forming a network, transmitting beacons on all available channels, periodically determining and exchanging RF characteristics at all individual nodes. However, such methods require transmission and reception of messages on different channels in a timed sequence, requiring implementation of sophisticated time synchronization algorithms, and may still have situations where some devices may fall out-of-sync and never recover.